1. Technical Field
This invention relates to a display arrangement for the charging condition in a strobing circuit of a photographic camera with a built-in strobe-flash device used to indicate that charging in the strobing circuit has been completed.
2. Prior Art
Recently the photographic camera with a built-in strobe-flash device has been popularized. The built-in strobe-flash device is usually adapted to be automatically discharged for an object to be photographed having a luminance lower than a predetermined level. However, should a main capacitor for the strobe-flash device have been insufficiently charged at a moment of such photographing, it would be impossible for the store-flash device to emit a predetermined intensity of light, and this might result in underexposure.
To avoid such inconvenience, most of the conventional cameras with built-in strobe-flash devices have been provided with display means serving to indicate whether the main capacitor in the strobing circuit has been sufficiently charged. Such displays of prior art cameras are usually provided in the form of a display lamp comprising a neon tube, or the like, included in the strobing circuit, which is partially visible through the outer wall of the camera, for example, adjacent the view-finder window or on the top of the camera, and the display lamp is turned on upon completion of charging.
With the conventional camera of the type mentioned above, it has been required to turn off the display lamp during nonuse of the camera regardless of whether the strobing circuit is in a sufficiently charged state or not, since the display lamp remaining turned on during nonuse of the camera is confusing for a user. To meet such a requirement, the circuit serving to turn the display lamp on has conventionally comprised, as shown by FIG. 5 of the accompanying drawings, a neon tube 2 electrically connected in parallel to a main capacitor 1 of the strobing circuit, and an NPN transistor 3 having its collector electrically connected to the neon tube 2, its emitter grounded, and its base electrically connected through a resistor 7 between a main switch 5 electrically connected to a power source 4, on one hand, and a release switch electrically connected in series with the main switch 5, on the other hand. A junction between the main switch 5 and the release switch 6 is electrically connected through the resistor 7 and a resistor 8 to the emitter of transistor 3. It should be understood that the main capacitor 1 for the strobe-flash device is always charged.
The transistor 3 is turned ON as the main switch 5 is closed to its 0N position and the neon tube 2 is turned on when the main capacitor 1 has been charged to a sufficient voltage level. Opening the main switch 5 to its OFF position causes the transistor 3 to be turned OFF and consequently the neon tube 2 is turned off.
However, it will be apparent from FIG. 5 that it has been required for the conventional display arrangement described above to turn on or off the neon tube 2 in response to the state of the main capacitor 5. To achieve this, the strobing circuit has had to include additional circuit elements such as the transistor 3 serving to switch the neon tube 2 and is thus correspondingly complicated.